1,004 research outputs found
Neutrino oscillations and gamma-ray bursts
If the ordinary neutrinos oscillate into a sterile flavor in a manner
consistent with the Super-Kamiokande data on the zenith-angle dependence of
atmospheric mu-neutrino flux, an energy sufficient to power a typical cosmic
gamma-ray burst (GRB) (about 10^{52} erg) can be carried by sterile neutrinos
away from the source and deposited in a region relatively free of baryons.
Hence, ultra-relativistic bulk motion (required by the theory of and
observations of GRBs and their afterglows) can easily be achieved in the
vicinity of plausible sources of GRBs. Oscillations between sterile and
ordinary neutrinos would thus provide a solution to the ``baryon-loading
problem'' in the theory of GRBs
Gamma-ray burst beaming: a universal configuration with a standard energy reservoir?
We consider a gamma-ray burst (GRB) model based on an anisotropic fireball
with an axisymmetric power-law distribution of the energy per solid angle with
index -k, and allow for the observer's viewing direction being at an arbitrary
angle with respect to the jet axis. This model can reproduce the key features
expected from the conventional on-axis uniform jet models, with the novelty
that the achromatic break time in the broadband afterglow lightcurves
corresponds to the epoch when the relativistic beaming angle is equal to the
viewing angle rather than to the jet half opening angle. If all the GRB
fireballs have such a similar energy distribution form with 1.5 < k < (or \sim)
2, GRBs may be modeled by a quasi-universal beaming configuration, and an
approximately standard energy reservoir. The conclusion also holds for some
other forms of angular energy distributions, such as the Gaussian function.Comment: Slightly expanded version accepted for publication in Ap
Constraints on the Redshift and Luminosity Distributions of Gamma Ray Bursts in an Einstein-de Sitter Universe
Two models of the gamma ray burst population, one with a standard candle
luminosity and one with a power law luminosity distribution, are chi^2-fitted
to the union of two data sets: the differential number versus peak flux
distribution of BATSE's long duration bursts, and the time dilation and energy
shifting versus peak flux information of pulse duration time dilation factors,
interpulse duration time dilation factors, and peak energy shifting factors.
The differential peak flux distribution is corrected for threshold effects at
low peak fluxes and at short burst durations, and the pulse duration time
dilation factors are also corrected for energy stretching and similar effects.
Within an Einstein-de Sitter cosmology, we place strong bounds on the evolution
of the bursts, and these bounds are incompatible with a homogeneous population,
assuming a power law spectrum and no luminosity evolution. Additionally, under
the implied conditions of moderate evolution, the 90% width of the observed
luminosity distribution is shown to be < 10^2, which is less constrained than
others have demonstrated it to be assuming no evolution. Finally, redshift
considerations indicate that if the redshifts of BATSE's faintest bursts are to
be compatible with that which is currently known for galaxies, a standard
candle luminosity is unacceptable, and in the case of the power law luminosity
distribution, a mean luminosity < 10^57 ph s^-1 is favored.Comment: Accepted to the Astrophysical Journal, 18 pages, LaTe
A Planning Pipeline for Large Multi-Agent Missions
In complex multi-agent applications, human operators are often tasked with planning and managing large heterogeneous teams of humans and autonomous vehicles. Although the use of these autonomous vehicles broadens the scope of meaningful applications, many of their systems remain unintuitive and difficult to master for human operators whose expertise lies in the application domain and not at the platform level. Current research focuses on the development of individual capabilities necessary to plan multi-agent missions of this scope, placing little emphasis on the integration of these components in to a full pipeline. The work presented in this paper presents a complete and user-agnostic planning pipeline for large multiagent missions known as the HOLII GRAILLE. The system takes a holistic approach to mission planning by integrating capabilities in human machine interaction, flight path generation, and validation and verification. Components modules of the pipeline are explored on an individual level, as well as their integration into a whole system. Lastly, implications for future mission planning are discussed
ANCHOR: web server for predicting protein binding regions in disordered proteins
Summary: ANCHOR is a web-based implementation of an original method that takes a single amino acid sequence as an input and predicts protein binding regions that are disordered in isolation but can undergo disorder-to-order transition upon binding. The server incorporates the result of a general disorder prediction method, IUPred and can carry out simple motif searches as well
Microstructural and Corrosion Properties of Cold Rolled Laser Welded UNS S32750 Duplex Stainless Steel
The main goal of this work was to study the effect of plastic deformation on weldability of duplex stainless steel (DSS). It is well known that plastic deformation prior to thermal cycles can enhance secondary phase precipitation in DSS which can lead to significant change of the ferrite-austenite phase ratio. From this point of view one of the most important phase transformation in DSS is the eutectoid decomposition of ferrite. Duplex stainless steels (DSSs) are a category of stainless steels which are employed in all kinds of applications where high strength and excellent corrosion resistance are both required. This favorable combination of properties is provided by their biphasic microstructure, consisting of ferrite and austenite in approximately equal volume fractions. Nevertheless, these materials may suffer from several microstructural transformations if they undergo heat treatments, welding processes or thermal cycles. These transformations modify the balanced phase ratio, compromising the corrosion and mechanical properties of the material. In this paper, the microstructural stability as a consequence of heat history due to welding processes has been investigated for a super duplex stainless steel (SDSS) UNS S32750. During this work, the effects of laser beam welding on cold rolled UNS S32750 SDSS have been investigated. Samples have been cold rolled at different thickness reduction (\u3b5 = 9.6%, 21.1%, 29.6%, 39.4%, 49.5%, and 60.3%) and then welded using Nd:YAG laser. Optical and electronical microscopy, eddy\u2019s current tests, microhardness tests, and critical pitting temperature tests have been performed on the welded samples to analyze the microstructure, ferrite content, hardness, and corrosion resistance. Results show that laser welded joints had a strongly unbalanced microstructure, mostly consisting of ferritic phase (~60%). Ferrite content decreases with increasing distance from the middle of the joint. The heat-affected zone (HAZ) was almost undetectable and no defects or secondary phases have been observed. Both hardness and corrosion susceptibility of the joints increase. Plastic deformation had no effects on microstructure, hardness or corrosion resistance of the joints, but resulted in higher hardness of the base material. Cold rolling process instead, influences the corrosion resistance of the base material
Effect of Primordial Black Holes on the Cosmic Microwave Background and Cosmological Parameter Estimates
We investigate the effect of non-evaporating primordial black holes (PBHs) on
the ionization and thermal history of the universe. X-rays emitted by gas
accretion onto PBHs modify the cosmic recombination history, producing
measurable effects on the spectrum and anisotropies of the Cosmic Microwave
Background (CMB). Using the third-year WMAP data and FIRAS data we improve
existing upper limits on the abundance of PBHs with masses >0.1 Msun by several
orders of magnitude. Fitting WMAP3 data with cosmological models that do not
allow for non-standard recombination histories, as produced by PBHs or other
early energy sources, may lead to an underestimate of the best-fit values of
the amplitude of linear density fluctuations (sigma_8) and the scalar spectral
index (n_s). Cosmological parameter estimates are affected because models with
PBHs allow for larger values of the Thomson scattering optical depth, whose
correlation with other parameters may not be correctly taken into account when
PBHs are ignored. Values of tau_e=0.2, n_s=1 and sigma_8=0.9 are allowed at 95%
CF. This result that may relieve recent tension between WMAP3 data and clusters
data on the value of sigma_8. PBHs may increase the primordial molecular
hydrogen abundance by up to two orders of magnitude, this promoting cooling and
star formation. The suppression of galaxy formation due to X-ray heating is
negligible for models consistent with the CMB data. Thus, the formation rate of
the first galaxies and stars would be enhanced by a population of PBHs.Comment: 17 pages (Apj style), 9 figures, submitted to Ap
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